It is of large importance to recover important base metals more effectively from resources regarded as secondary ones, such as slag, low or medium grade ores, mill scale and scrap. Further, there are important mineral deposits that are not processed due to the inherent difficulties to technically and economically concentrate and extract the valuable metals in these deposits. One example of deposits, which are difficult to process and exploit, is laterites containing nickel or cobalt, in which the nickel and cobalt partly are bound and finely dispersed in silicates.
For many years, chlorination has been considered an effective process for recovering metal values from ores, slag, scrap and other material. Chloride process metallurgy is of large industrial importance in the production of titanium and zirconium metal.
U.S. Pat. No. 4,144,056 discloses a process for recovering nickel, manganese and cobalt from e.g. silicate ores, such as laterites, by heating the ore in an chloride melt containing ferric chloride and ammonium chloride or alkali chloride, such as sodium chloride. The nickel in the laterite ores is present both as nickel oxide and as nickel oxide in the silicate phase. The oxides of nickel, manganese and cobalt present in the laterite ore react in the salt melt with the ferric chloride under formation of iron oxide and dichlorides of nickel, manganese, and cobalt. The nickel, manganese, and cobalt chlorides are then leached with water and recovered.
Ocean-floor nodules are potentially the most important valuable source of industrial metals, such as copper, nickel, cobalt and manganese. U.S. Pat. No. 4,144,056 describes also the recovery of these valuable metals from sea nodules by reacting ground nodules with ferric chloride and sodium chloride at 420° C. The salt melt with the added sea nodules was subsequently cooled and water leached, whereby the manganese, cobalt, copper and nickel was recovered.
Extraction of cobalt, copper, iron, manganese and iron from Pacific Ocean deep sea nodules using chloride salt melts has also been reported by S. Von Winbush and V. A. Maroni in Separation Science and Technology Volume 22 (2&3) pp. 1135-1148 (1987) and U.S. Pat. No. 4,762,694. These authors report that preferred salt melts were eutectics of LiCl, NaCl, KCl, and MgCl2 with the eutectic temperature at or below about 400° C. The transition metals were subsequently recovered by distillation, electrolytic deposition, and by oxidation and precipitation as an oxide.
In U.S. Pat. No. 4,179,492, a process is disclosed, where rare earth metal oxides are chlorinated in a salt melt comprising ferric chloride and at least one other chloride from the group consisting of alkali metal chlorides, alkaline earth metal chlorides, zinc chloride and ammonium chloride.
Chlorination of sulfide ores of lead, zinc, copper, silver and gold is disclosed in U.S. Pat. No. 4,209,501 and is carried out by a process comprising reaction of the sulfide ore in salt melts. This consists of at least two different chlorides with one chloride comprising 15% by weight and being selected from the group consisting of ferric chloride, ferrous chloride, cupric chloride, cuprous chloride and mixtures thereof, and at least one other chloride from the group consisting of alkali metal chlorides, alkaline earth metal chlorides, zinc chloride and ammonium chloride. It is further mentioned in U.S. Pat. No. 4,209,501 that chlorine gas or sulfur chloride may be introduced in the salt melt as chlorine donor.
U.S. Pat. No. 5,074,910 discloses the recovery of precious metals from sulfide ores by chlorination in a salt melt of potassium chloride and cuprous chloride. The reaction is carried out in the temperature range 300° C. to 600° C.
In U.S. Pat. No. 4,576,812, a process is disclosed for making chlorides from sulfides of copper, iron, lead, zinc, silver and gold by chlorination in ferric chloride, cupric chloride or a mixture of ferric and cupric chloride. The metal sulfides are recovered as metal chlorides and elemental sulfur.
SE 381 862 describes a chlorination process for the high temperature metals titanium, silicon, vanadium, niobium, tantalum, tungsten and molybdenum, or alloys that contain these metals. The chlorination is carried out in a salt melt containing sodium chloride and/or potassium chloride and in addition chlorides of iron, copper and chromium. Characteristic of this process is that liquid chlorine is added to the salt melt.
U.S. Pat. No. 6,274,104 B1 discloses a method for recovering non-ferrous metals, particularly nickel, cobalt, copper, zinc, manganese and magnesium, from materials containing said metals by converting said non-ferrous metals into sulfates by means of melt and melt coating sulfation, i.e. by a thermal treatment under oxidizing conditions within a temperature range of 400 to 800° C., during which a reaction mixture is formed containing at least one said non-ferrous metal, iron(III)sulfate and alkali metal sulfate, and appropriate reaction conditions are selected to substantially prevent iron(III)sulfate from thermally decomposing to hematite, and finally, said non-ferrous metals are recovered as metallic compounds.
A process for recovering precious metals from sulfide ores is disclosed in U.S. Pat. No. 5,074,910. The process involves chlorinating a mixture of an ore concentrate and salt to form a liquid melt. The salt preferably contains potassium chloride. This chlorination is carried out at a temperature between 300° C. and 600° C. while stirring. The process converts precious metals in the elemental and sulfide forms into precious metal chlorides which are recovered by subsequent processing steps.
GB 1 471 009 discloses a process for recovering a base metal, i.e. manganese, iron, cobalt, nickel, copper, zinc, tin, or lead, dissolved as a chloride in molten salt comprising an alkali metal or alkaline earth metal chloride or mixture of such chlorides, in a process in which the base metal values are precipitated by means of hydrogen, hydrogen sulfide or both and are separated as a liquid phase from the molten salt.
JP 2002-372518 discloses that platinum group elements (ruthenium, osmium, iridium and rhodium) in a sample can be determined by placing the sample in a crucible together with nickel powder, sulfur powder, sodium carbonate, borax and silica sand, mixing the ingredients in the crucible, heating them to melt, and then cooling the melt to obtain a nickel sulfide button, which then is used for determining the platinum group elements.
U.S. Pat. No. 4,475,993 describes treatment of fine grained industrial fly ash having a silicate base to recover valuable trace metals such as gallium, silver and the like in concentrations less than about 1 wt %. The fly ash is contacted with AlCl3 in an alkali halide melt. Example 1 discloses a dosage of AlCl3 of about one mole % and an attack of the silicate base should be avoided.
A process for recovery of platinum group metals (PGMs) from refractory ceramic substrates containing an aluminum silicate and/or alumina, for example, wash-coated auto emission control catalysts and Pt reforming catalysts is disclosed in GB 2 067 599 A. To carry out the process, a charge, in divided form, containing the substrate, one or more fluxes and a collector material is heated in a high intensity furnace, preferably of the plasma arc type, to a temperature of at least 1420° C. to produce a molten metallic phase including a substantial proportion of said metals and a molten slag phase. These are then separated and the platinum group metals subsequently extracted from the metallic phase. The preferred fluxes are selected from CaO, CaF2, BaO, Fe2O3, MgO, SiO2 and TiO2, and the preferred collector material is selected from Fe, Ni, Cu, Co, Pb, Zn, and Al or mixtures thereof.
Pure metals, alloys, oxides, sulfides, carbonates and silicates react in molten chloride salt melts with chlorine and chlorine donors such as ferric chloride and cupric chloride under the formation of metal chlorides. However, the present state of the art related to chlorination of metal resources suffers sometimes from low reaction rates and low yield of valuable metals that prevail in the ore that is chlorinated in the salt melt.
Thus, it is well known that metal values can be recovered from many sources such as scrap, ores and sea nodules by chlorination. The formed metal chlorides can subsequently be separated and extracted by fractional distillation and condensation, electrolysis of the salt or by hydrometallurgical processing.
There are three groups of chlorination processes:    a) Chlorination of solid raw materials such as sulfide, silicate and oxide ores as well as ocean floor nodules by gaseous chlorine.    b) Chlorination of ores, scrap, mill scale, dust etc. in salt melts in the absence of chlorine. Here, ferric chloride and/or cupric chloride are commonly used chlorine donors.    c) The same as b) but in the presence of elemental chlorine, which can be added as chlorine gas or liquid chlorine.
However, in prior art chlorination processes of the b) kind, the reaction rate and mostly also the yield of valuable metals are unacceptably low.